In the diaper industry, diapers are made from a continuous strip of flat unfinished diaper blanks; finish component parts, normally of elastic material, are applied to the strip; and the strip is cut crosswise into a succession of flat finished diapers.
More specifically, one of the finish component parts comprises lateral panels, which have a portion of adhesive or Velcro-type material, and are applied to the sides of each diaper blank to connect the ends of the diaper, when worn, into an annular belt.
The lateral panels—to which the following description refers purely by way of example—are normally formed from a continuous strip of elastic material which is fed along a path, extending through a number of work stations, by conveying means normally defined by conveyor rollers, about which the strip is partly wound.
Though effective and widely used on diaper manufacturing machines, the above method has several drawbacks, on account of the irregular shape of the path, the pull exerted on the strip by the conveyor rollers, and the stress to which the strip is subjected at the work stations, resulting in increasing and decreasing tension of the strip as it travels along the path, and, given the elasticity of the strip material, in inevitable uncontrolled slippage of the material.
Because the work stations are synchronized with one another and the strip must be maintained in a predetermined position, as it travels along the path, to ensure it is positioned correctly on entering each work station, provision is made, along the path, for position sensors, and compensating stations connected to the sensors to correct any variation in the tension of the material and so prevent the strip from deviating from the correct position.
The sensors and compensating stations obviously complicate the machine mechanically, thus impairing reliability and greatly increasing the cost and overall size of the machine.
Though to a lesser degree, the above problem is also encountered when using strip material that is not exactly elastic and visibly stretchable, but nevertheless has a certain degree of intrinsic elasticity.